New form of indigo readily soluble in vats and method of making same.



UNITED STATES PATENT QEETQE.

RUDOLF KNIETSCH AND PAUL SEIDEL, OF LUI)WIGSHAFEN-ON-RHINE,

GERMANY, ASSIGNORS TO OF SAME PLACE.

THE BADISOHE ANILIN AND SODA-FABRIK,

NEW FORM OF INDIGO READILY SOLUBLE IN VATS AND METHOD OF MAKING SAME.

SPEGIFICA TIGN forming part of Letters Patent No. 671,344, dated April2, 1901.

Application filed May 21, 1900- Serial No. 17,455. (Specimena) T ctZZwhom, it may concern..-

Be it known that we, RUDoLF KNIETSGH, a subject of the King of Prussia,German Emperor, and PAUL SEIDEL, a subject of the King of Saxony,doctors of philosophy, residing at Ludwigshafen-on-Rhine, in the Kingdomof Bavaria and Empire of Germany, have invented new andusefullmprovementsin aNew Form oflndigo Readily Soluble in the Vat andMethod of Making Same, of which the following is a specification.

It is well known that dry vegetable indigo in the form in which it isusually put upon the market must be ground in specially-constructedmills in order to bring it to a condition in which it will readily andcompletely dissolve in the indigovat. This grinding operation isfrequently prolonged for days. Synthetic indigo also under someconditions separates out d uring its manufacture in a crystallinecondition, and the crystals may be of such a size as to injnriouslyaffect the ready solubility of the indigo in the vat. We have discoveredthat indigo which is with difficulty soluble in the vat, irrespective ofits origin, can by a simple treatment be converted into a new form ofindigo which can be readily dissolved.

The new process according to our invention consists in treating indigowith sulfuric acid under such conditions of concentration that nosulfonation of the indigo takes place, while a sulfate of indigo orloose combination of sulfuric acid therewith is formed. For this purposesulfuric acid containing about sixty-five to eighty-five per cent. H SOcan be employed. This sulfate so obtained crystallizes in the form ofblack-brown needles. This body is treated with water, when it decomposesand the regenerated indigo separates out in a physical condition that isfitted for use in all kinds of vats, it being easily soluble even in thefermentation-vat, which acts particularly mildly. The new readilysolubleproduct is chemically indigo; but its physical condition is changed bythe treatment, so that from an industrial standpoint it becomessubstantially a new product.

The following table will illustrate the difference between our new formof indigo and indigo in the known form:

New form of indigo Old indigo paste. m paste Brown-red, with abronze-like luster.

Color Blue to blue-black Change on treating a twenty-percent.

paste with- (1) Sulfuric acid.

(2) Caustic soda Painted onto glass and dried.

Does not become essentially thicker.

Does not become essentially thinner.

Red, with a bronzelike luster.

Becomes thicker Becomes thinner.

Blue to reddishblue color.

Or, to explain more fully the above tests, we have identifiedaspecimenof our new product as follows: If we make twenty grams of the dryproduct into a paste with eighty cubic centimeters of water itconstitutes a very fluid mass. If to such a paste we add one cubiccentimeter of sulfuric acid of live (5) degrees Baum and heat it to atemperature of about thirty degrees centigrade the paste does not becomeessentially thicker, while a paste of ordinary indigo is by thistreatment converted into a thicker mass. If we take another similarportion of twenty (20) per cent. paste of our new product and mix itwith one cubic centimeter of caustic soda-lye of five (5) degrees Baumand heat it to a temperature of about thirty (30) degrees centigrad e,the original very fluid mass does not become essentially thinner, whilea paste of indigo in the ordinary form under similar treatment becomesdistinctly thinner than it was.

The following example will serve to illustrate the manner in which ourinvention is carried into practical effect and our new vatsoluble indigois obtained:

Stir about one hundred (100) parts of dry indigo in the form of powderinto about five hundred (500) parts of sulfuric acid containingseventy-five percent. H Warm the mixture while carefully stirring toabout thirty degrees centigrade. When the mixture is affected so that auniform paste is ob tained, allow the mass to stand for about an hour.The sulfate of indigo is then formed. To obtain the indigo in theaforesaid new physical condition, add to the entire mass about twothousand (2,000) parts of water. Stir well, collect the new indigo byfiltration, and wash until free from acid. The new indigo retains itsvaluable property of ready solubility in the vat even after drying.

Now what we claim is l. The improvement in the art of expediting thesolubility of indigo which consists in combining with it sulfuric acidto a point below sulfonation and then decomposing with water,substantially as described.

2. As a new product the new form of indigo readily soluble in the vatwhich can be obtained by treatingindigo with sulfuric acid RUDOLFKNIETSGH. PAUL SEIDELL Witnesses:

ERNEST F. EHRHARDT, J. L. HEINKE.

